In general, for shoes with an air refreshing system, check valves or unidirectional air inlet and outlet valves are installed at the heel of the shoes. For example, there is disclosed in U.S. Pat. No. 5,138,775, incorporated herein by reference, a unidirectional air valve located in a wall defining an air chamber in a heel of a shoe. The air chamber is compressed or is resiliently restored to the original state from a compressed state by normal walking. Thus, the air in the air chamber can be pushed to the shoe or the air out of a shoe can be absorbed into the shoe through the air inlet valve.
In the prior art air valves, a removable diaphragm is located in a longitudinal slot located on or in a lateral side of a transverse air hole. By using the diaphragm, the air valve can then be converted into a check valve, sometimes referred to as a unidirectional valve or device.
However, since the transverse air hole and longitudinal slot of the air valve are integrally formed at the periphery of the air chamber at sole, the mold for the air hole and slot is very complex and thus bears a high cost.